chapter 11: cell signaling II Flashcards
what are the components of a signal transduction pathway?
- the signal (ligand)
- a receptor of the signal: protein
- response to signal
what are the steps of signal transduction?
- reception
- transduction
- response
signal reception
the signal (ligand) binds to the receptor of the signal
how is the response to the signal created after the ligand binds to the receptor?
the receptor changes shape
is the ligand changed after binding?
no
is the receptor always active?
no, it alternates between active and inactive conformations
is the binding of the ligand to receptor reversible?
yes
are receptor proteins highly specific for their ligands?
yes
what type of receptor do polar/large signals have?
transmembrane protein: a receptor that is embedded in the membrane because the signal cannot diffuse through the cell membrane on its own
what type of receptor do nonpolar signals have?
an intracellular receptor that is in the cytosol or nucleus because nonpolar signals can diffuse directly across the lipid bilayer of the cell membrane
what happens after ligand binding causes the receptor to change shape?
reveals NLS tag to enter nucleus where it affects protein making
- receptor is considered the transducer and effector
are all receptors are transducers and effectors?
no, it usually does not produce the effect
what happens when the receptor does not act as an effector?
after the receptor binds to the ligand, it starts a chain of signaling that eventually creates a response
two types of receptors that start a chain of signaling
- G-Protein Coupled Receptors
- Receptor Tyrosine Kinases
G-Protein Coupled Receptors
the receptor that binds to the signal, which gets binded to GTP to activate the G-protein
GTP
nucleotide important for cell signaling
GEF
GDP/GTP exchange
GAP
GTP hydrolysis
steps of G-Protein Coupled Receptors
- signal enters the GPCR
- inactive form of G protein has GDP bound
- activation of G protein by binding with receptor and exchange of GDP for GTP
- activated G-protein moves through cell membrane and binds/activates next protein
Receptor Tyrosine Kinases
enzyme-linked cell-surface receptors that phosphorylate themselves after binding a signaling molecule
protein kinase
adds a phosphate group to proteins and causes enzyme to change shape and open active site, which allows the substrate to bind to it
phosphatases
removes phosphate groups from proteins
steps of receptor tyrosine kinases
- kinases add phosphate to change shape of proteins
- shape change can reveal binding site so protein can phosphorylate/activate the next protein in the signaling pathway
signal transduction
a series of molecular switches turn each other on by changing next molecule in pathway
are more than one responder or transducing protein may be involved?
YES
can more than one second messenger relay the signal from the receptor in the membrane to other regions in the cell?
yes and they can also amplify the signal
kinase cascades
add/remove phosphates using kinase and phosphatase
what activates a kinase?
Ras triggers its phosphorylation
what does the active kinase start?
phosphorylation cascade
phosphorylation cascade
each kinase phosphorylates a different kinase until a response is triggered in the cell
why is signaling amplified?
- larger cellular response
- more molecules impacted
- multiple response can be made simultaneously
what are two kinds of second messengers?
cAMP and DAG + IP3
cAMP
adenylyl cyclase gets activated to transform ATP into cAMP
what is adenylyl cyclase?
a membrane protein
steps of cAMP activation
- GPCR binds ligand. GEF exchange GDP for GTP on G-protein
- activated G-protein migrates to adenylyl cyclase and turns it on creating cAMP 2nd messengers
- cAMP binds to channel protein, opening and allowing ions to travel down their concentration gradient
fight or flight response using adenylyl cyclase
- epinephrine (signal and 1st messenger)
- cAMP (second messenger)
- activates glycogen phosphorylase to release glucose allowing it to help create a fight or flight response
PIP2
DAG + IP3
what does phospholipase C do when activated?
cleaves PIP2, releasing the secondary messengers IP3 and DAG
what do IP3 and DAG do?
activate different cellular responses
what can dag initiate?
exocytosis
what can IP3 initiate?
release of Ca2+ ions from smooth ER
signal response
cells respond to signals by activating enzymes, opening membrane channels or initiating gene expression
what does cell response depend on?
signal and cell type
what kind of responses do second messengers produce?
slow and fast responses
what do complex multi-component signal transduction pathways provide?
- opportunities for feedback
- signal amplification
- interactions inside one cell between multiple signals and signaling pathways
what two ways can signals activate?
- active when phosphorylated by both pathways
- active when phosphorylated by either pathway
are enzymes always active?
no, cells regulate the activity of transducer molecules to respond to signal and then return to inactive state
